The present invention generally relates to the field of batteries, in particular the present invention is directed to a novel battery having a collapsing vent system and overcharge protection.
A persistent problem associated with the design of many types of sealed batteries is that under certain conditions the internal pressure generated by the electrochemical system contained within the sealed battery causes the battery to explode. This problem occurs in Lithium-ion cells as well as other battery types. The excessive internal pressure may be created by a chemical reaction or by the expansion of gases within the battery due to the presence of excessive heat. Alternatively, the battery may explode if there is a short circuit, if the battery is recharge too rapidly, or if the battery is recharged over an extended period of time. Therefore, it is important to have a safety mechanism for venting pressurized gases from the battery before a dangerous situation is encountered.
In some existing battery venting mechanisms, the vent is a separate part welded to one end of the cell. This type of system has flow limitations because it allows the battery to vent at only one end of the cell. Thus, when this type of battery has a fast thermal reaction, the vent opening can become clogged causing the cell enclosure to rupture and the cell components to burn.
A related problem is that existing batteries do not have an overcharge protection that is part of the battery""s structure. Generally, the only overcharge protection is provided by an active device associated with the battery pack electronics. This lack of protection is a serious concern because a dangerous condition exists if a battery remains at an overcharged state or continues to charge during venting of excessive heat or pressurized gases. Furthermore, if a safety feature could prevent the pressure within the battery from reaching a level where venting is required, a dangerous situation would be avoided without the release of gases.
The present invention is directed to eliminating the above problems associated with existing batteries, and more specifically battery venting mechanisms, through the use of a novel venting device and overcharge protection system. The present invention avoids the above problems associated with existing vent mechanisms by employing a number of novel features, which will be discussed here briefly, and in more detail below.
The battery casing has an inner tube that completely surrounds a hollow core and an outer tube that surrounds the inner tube. The inner tube is connected at both ends to two end plates. The inner tube, outer tube, and end plates form a sealed, hermetic annular space in which the battery components are held. The inner tube is designed to collapse into the hollow core when a pressure inside the annular space exceeds a predetermined collapsing pressure, and the welds connecting the inner tube to the end plates are designed to break when the pressure inside the annular space exceeds a predetermined breaking pressure.
In addition, the invention can take advantage of the fact that the inner tube is negatively charged by have a connecting member, which is electrically connected to the anode and thus positively charged, that extends into the hollow core. When the negatively charged inner tube collapses, it makes contact with the positively charged connecting member, to provide a short circuit for reducing the voltage of the battery.